Strong Fermi Resonance Associated with Proton Motions Revealed by Vibrational Spectra of Asymmetric Proton-Bound Dimers

Qian Rui Huang, Ryunosuke Shishido, Chih Kai Lin, Chen Wei Tsai, Jake A. Tan, Asuka Fujii, Jer Lai Kuo

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)

Abstract

Infrared spectra for a series of asymmetric proton-bound dimers with protonated trimethylamine (TMA-H+) as the proton donor were recorded and analyzed. The frequency of the N–H+ stretching mode is expected to red shift as the proton affinity of proton acceptors increases. The observed band, however, shows a peculiar splitting of approximately 300 cm−1 with the intensity shifting pattern resembling a two-level system. Theoretical investigation reveals that the observed band splitting and its extraordinarily large gap of around 300 cm−1 is a result of strong coupling between the fundamental of the proton stretching mode and overtone states of the two proton bending modes, that is commonly known as Fermi resonance (FR). We also provide a general theoretical model to link the strong FR coupling to the quasi-two-level system. Since the model does not depend on the molecular specification of TMA-H+, the strong coupling we observed is an intrinsic property associated with proton motions.

Original languageEnglish
Pages (from-to)1936-1941
Number of pages6
JournalAngewandte Chemie - International Edition
Volume60
Issue number4
DOIs
Publication statusPublished - 2021 Jan 25

Keywords

  • Fermi resonance
  • IR spectroscopy
  • ab initio calculations
  • anharmonic coupling
  • hydrogen bonds

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)

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